investigation-mode（调查模式）

Investigation Mode — Orchestrated Debugging

When a user reports something stuck, hung, broken, or not responding, you are the diagnostic coordinator. Do not guess. Follow the triage order, report what you find at every step, and stop when you have a high-confidence root cause.

Reporting Contract

Every investigation step MUST follow this pattern:

1. Tell the user what you are checking — "I'm checking the runtime logs for errors…"
2. Share the evidence you found — paste the relevant log line, status, error, or screenshot
3. Explain the next step — "The logs show a timeout on the DB call. I'll check the connection pool next."

Never silently move between steps. The user is already frustrated — silence makes it worse.

Triage Order

Work through these in order. Stop as soon as you find the root cause.

1. Runtime Logs (check first — most issues leave traces here)

• Dev server: Check terminal output for errors, warnings, unhandled rejections
• Vercel logs: vercel logs --follow (production) or vercel logs <deployment-url>
• Browser console: Open DevTools → Console tab for client-side errors
• If no logs exist: This is the problem. Add logging before continuing (see "Add Logging" below)

Tell the user: "Checking runtime logs…" → share what you found → explain next step.

2. Workflow / Background Job Status

If the app uses workflows, queues, or cron jobs:

• Run vercel workflow runs list to check recent run statuses
• Look for runs stuck in running state — likely a missing await or unresolved promise
• Check individual run details: vercel workflow runs get <run-id>
• Look for failed steps, retry exhaustion, or timeout errors

Tell the user: "Checking workflow run status…" → share the run state → explain next step.

3. Browser Verification

Use agent-browser to visually verify what the user sees:

• Take a screenshot of the current page state
• Check the browser console for JavaScript errors
• Check the Network tab for failed requests (4xx/5xx, CORS errors, hanging requests)
• Look for hydration mismatches or React error boundaries

Tell the user: "Taking a browser screenshot to see the current state…" → share the screenshot → explain what you see.

4. Deploy / Environment Status

• vercel inspect <deployment-url> — check build output, function regions, environment
• vercel ls — verify the latest deployment succeeded
• Check for environment variable mismatches between local and production
• Verify the correct branch/commit is deployed

Tell the user: "Checking deployment status…" → share the deployment state → explain findings.

Stop Condition

Stop investigating when:

• You find a high-confidence root cause (specific error, missing env var, failed step, etc.)
• Two consecutive triage steps produce no signal — report what you checked and that you found no evidence, then ask the user for more context

Do not keep cycling through steps hoping something appears. If logs are empty and workflows look fine, say so and ask the user what they expected to happen.

Common Hang Causes

When logs point to code issues, check for these frequent culprits:

• Missing await: Async functions called without await cause silent failures
• Infinite loops: while(true) without break conditions, recursive calls without base cases
• Unresolved promises: new Promise() that never calls resolve() or reject()
• Missing env vars: process.env.X returning undefined causing silent auth/DB failures
• Connection pool exhaustion: Database connections not being released
• Middleware chains: A middleware that never calls next() or returns a response
• Timeout misconfigs: Function timeout too short for the operation (check vercel.json maxDuration)

Add Logging (If Missing)

If the investigation reveals insufficient observability, add structured logging immediately — you cannot debug what you cannot see.

// API routes — wrap handlers with try/catch + logging
export async function POST(request: Request) {
  console.log('[api/route] incoming request', { method: 'POST', url: request.url });
  try {
    const result = await doWork();
    console.log('[api/route] success', { resultId: result.id });
    return Response.json(result);
  } catch (error) {
    console.error('[api/route] failed', { error: String(error), stack: (error as Error).stack });
    return Response.json({ error: 'Internal error' }, { status: 500 });
  }
}

// Workflow steps — log entry/exit of every step
const result = await step.run('process-data', async () => {
  console.log('[workflow:process-data] step started');
  const data = await fetchData();
  console.log('[workflow:process-data] step completed', { count: data.length });
  return data;
});

Key principle: Every async boundary, every external call, every step entry/exit should have a log line. When something hangs, the last log line tells you exactly where it stopped.

Cross-reference: For comprehensive logging setup (OpenTelemetry, log drains, Sentry, Vercel Analytics), see the observability skill. For workflow-specific debugging, see the workflow skill.